At first I thought that the problem was me - this is a series that seemed very interesting based on the trailer alone, so I wondered if I my expectations were too big to begin with.
After watching 10 episodes (and having a hard time finishing the last two), I realized that the problem is in the series itself.

First of all, the idea that is supposed to be at the base of the series is not very clear. At the beginning I thought it would be some kind of spicy enemies-to-lovers story, but the ingredients weren't quite there - the reasons for Uea to dislike King so much are not solid enough to be convincing, and King's opinion of Uea at the beginning is a complete mystery. When the FWB situation started, I hoped that these things would be explored more as the series went on, but it never happened.
Instead of that, the story took an unexpected turn as it revealed Uea's turbulent past. I didn't mind the presence of such themes, but I was expecting them to be taken seriously and to be explored properly, which (again) never happened. If anything, it looked more like whoever wrote the story wanted Uea to have as many traumatic experiences and toxic people in his life as possible. I started to wonder if someone in the production team believes that "trauma is sexy" or something like that.
The series itself ended up failing with both the FWB story and the abuse survivor story, by never diving deep enough in either theme. The agreement between Uea and King becomes secondary very quickly, and Uea's problems only seem to grow in number. The relationships between the characters (not only Uea and King, but also their friends, colleagues and family) were also never shown properly, making their interactions always sound ambiguous - I was never sure whether one was supposed to be a close friend or a well-intentioned acquaintance. The miscommunication (which I was half hoping would not be there) and the awful pacing did the rest of the work to ruin it for me.
The acting is good enough, but since the story is so lacking in the first place, I was not able to enjoy it as much as I wished to. As for the music, it was too repetitive to add anything to the scenes. The sexy scenes were pretty mostly because the actors themselves looked pretty, I believe.

I was able to finish the whole thing thanks to some miracle, but I have no intention to touch this series ever again. I wish the writers chose one route and did it well instead of adding so many elements and handling them so badly. Its potential was wasted entirely and I can't bring myself to recommend it to anyone at all.